This invention relates to compressed gas cylinders, and provides a method and apparatus for maintaining the contents of such cylinders at a desired temperature. The invention is especially useful with cylinders that contain calibration gas mixtures.
A calibration gas is a gas mixture which contains a plurality of components in known proportions. A calibration gas may be used to calibrate gas analyzers or the like. By passing the calibration gas through a gas analyzer, and observing the readings taken from the analyzer, one can adjust the analyzer so that it indicates the correct proportion of each component in the mixture. Typically, a calibration gas is provided in a compressed gas cylinder.
In order to serve its intended purpose, all of the components of a calibration gas must remain gaseous. If the cylinder containing the calibration gas is allowed to become too cold, some of the components of the gas can condense, rendering the mixture useless for calibration.
The problem of exposure of a gas cylinder to cold temperatures is not great in the laboratory, but can be serious in the field. For example, in the operation of gas pipelines, it is necessary to monitor the composition of the gas stream, and thus calibration gases are needed to insure the accuracy of the gas analyzers used. But such pipelines typically extend through remote and cold areas. Keeping a calibration gas cylinder in such remote areas, especially outdoors, without protection, could render the calibration gas useless.
One solution that has been proposed, to solve the above-described problem, is to wrap the cylinder in a special heating blanket. While the latter achieves the result of keeping the cylinder warm, it is cumbersome to affix the blanket to the cylinder, and in places where the ambient temperatures are very cold, the blanket is relatively inefficient. Moreover, it may present a safety hazard by applying heat directly to the cylinder, since many calibration gases are flammable, and gas cylinders can occasionally leak. Also, a heating blanket generally provides no means for heating the cylinder valve and regulator. Thus, even if the cylinder is adequately heated by a blanket, the contents of the cylinder may be cooled again when they pass through the unheated valve and regulator.
The present invention solves the problems described above, by providing a safe and economical apparatus and method for maintaining the contents of a compressed gas cylinder at a desired temperature.